The present invention relates to a scroll fluid machine such as a scroll vacuum pump or a scroll compressor.
As disclosed in JP2004-28033A, a scroll fluid machine comprises a fixed scroll having a spiral fixed wrap and an orbiting scroll having a spiral orbiting wrap. The orbiting scroll is revolved by a driving shaft while the fixed wrap engages with the orbiting wrap. A compression chamber formed between the fixed and orbiting wraps is gradually decreased in volume and moved towards the center, thereby compressing a compression medium such as a gas sucked through an inlet in the outer circumference and discharging it through an outlet at the center.
The compression medium is compressed towards the center, so that the temperature of the center rises compared with the outer circumference. Thus, it is necessary to cool a central part so as to prevent a rotary part of the driving shaft and orbiting scroll such as bearings or seal member from deteriorating owing to heat.
However, in the scroll fluid machine, if the compression medium is a toxic gas that contaminates natural environment, it is necessary to use a sealed structure in which the driving shaft and surroundings thereof are completely sealed by a cover to prevent the compression medium from leaking to outside.
It is difficult to cool the inside of the sealed structure. So cooling is carried out by an external fan disposed outside. However, a central part cannot be cooled although outer parts are cooled. So heat is likely to deteriorate bearing or sealing members to make durability poor.